Powertrain of an automatic transmission

ABSTRACT

A powertrain of an automatic transmission includes a first planetary gear set having a double pinion planetary gear set, a second planetary gear set having a single pinion planetary gear set and a third planetary gear set having a double pinion planetary gear set to achieve eight forward speeds and two reverse speeds by combining the three planetary gear sets and six frictional elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Korean Patent ApplicationNumber 10-2008-0053363 filed Jun. 5, 2008, the entire contents of whichapplication is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a powertrain of an automatictransmission. More particularly, the present invention relates to apowertrain of an automatic transmission that enables eight forwardspeeds and two reverse speeds by combining three simple planetary gearsets and six frictional elements.

2. Description of Related Art

A typical shift mechanism of an automatic transmission utilizes acombination of a plurality of planetary gear sets. A gear train of suchan automatic transmission that includes the plurality of planetary gearsets changes rotating speed and torque received from a torque converterof the automatic transmission, and accordingly changes and transmits thechanged torque to an output shaft.

It is well known that when a transmission realizes a greater number ofshift speeds, speed ratios of the transmission can be more optimallydesigned and therefore a vehicle can have better fuel mileage and betterperformance. For that reason, an automatic transmission that enablesmore shift speeds is under constant investigation.

In addition, with the same number of speeds, features of a gear trainsuch as durability, efficiency in power transmission, and size depend alot on the layout of combined planetary gear sets. Therefore, designsfor a combining structure of a gear train are also under constantinvestigation.

A manual transmission that has too many speeds causes inconvenience ofexcessively frequent shifting operations to a driver. Therefore, thepositive features of more shift-speeds are more important for automatictransmissions because an automatic transmission automatically controlsshifting operations basically without needing manual operation.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY OF THE INVENTION

Various aspects of the present invention are directed to provide apowertrain of an automatic transmission having advantages of enablingeight forward speeds and two reverse speeds by combining three simpleplanetary gear sets and six frictional elements.

An exemplary embodiment of the present invention provides a powertrainof an automatic transmission that includes a first planetary gear sethaving a first operating member fixedly connected to a transmissioncase, a second operating member, and a third operating member fixedlyconnected to an input shaft, a second planetary gear set having a fourthoperating member selectively connected to the second operating member, afifth operating member, and a sixth operating member selectivelyconnected to the third operating member and the transmission case, athird planetary gear set having a seventh operating member selectivelyconnected to the second operating member, the input shaft, and thetransmission case, an eighth operating member fixedly connected to thesixth operating member, and a ninth operating member fixedly connectedto the fifth operating member and an output shaft, and a plurality offriction members that selectively connect operating members of thefirst, second, and third planetary gear sets, the input shaft, and thetransmission case.

The plurality of friction members may include a first clutch selectivelyconnecting the third operating member and the sixth operating member, asecond clutch selectively connecting the seventh operating member to theinput shaft, a third clutch selectively connecting the second operatingmember and the fourth operating member, a fourth clutch selectivelyconnecting the second operating member and the seventh operating member,a first brake selectively connecting the sixth operating member to thetransmission case, and a second brake selectively connecting the seventhoperating member to the transmission case.

The first planetary gear set may be a double pinion planetary gear sethaving operating members of a first sun gear, a first ring gear, and afirst planet carrier, the first sun gear acting as the first operatingmember, the first ring gear acting as the second operating member, andthe first planet carrier acting as the third operating member.

The second planetary gear set may be a single pinion planetary gear sethaving operating members of a second sun gear, a second planet carrier,and a second ring gear, the second sun gear acting as the fourthoperating member, the second planet carrier acting as the fifthoperating member, and the second ring gear acting as the sixth operatingmember.

The third planetary gear set may be a double pinion planetary gear sethaving operating members of a third sun gear, a third ring gear, and athird planet carrier, the third sun gear acting as the seventh operatingmember, the third ring gear acting as the eighth operating member, andthe third planet carrier acting as the ninth operating member.

It may be configured that the third clutch and the first brake operatefor a first forward speed, the third clutch and the second brake operatefor a second forward speed, the third clutch and the fourth clutchoperate for a third forward speed, the second clutch and the thirdclutch operate for the fourth forward speed, the first clutch and thethird clutch operate for a fifth forward speed, the first clutch and thesecond clutch operate for a sixth forward speed, the first clutch andthe fourth clutch operate for a seventh forward speed, the first clutchand the second brake operate for a eighth forward speed, the fourthclutch and the first brake operate for a first reverse speed, and thesecond clutch and the first brake operate for a second reverse speed.

According to the exemplary powertrain of an automatic transmission ofthe present invention, eight forward speeds and a reverse speed can beenabled by combining three simple planetary gear sets and six frictionalelements.

In addition, a large number of shift-speeds are enabled, and thus powerdelivery performance may be improved and fuel consumption may be reducedby effectively utilizing an engine power.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description of the Invention, which togetherserve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary powertrain of an automatictransmission according to the present invention.

FIG. 2 is an exemplary operational chart of a powertrain of an automatictransmission according to the present invention.

FIG. 3 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the first forward speed of a powertrainof an automatic transmission according to the present invention.

FIG. 4 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the second forward speed of a powertrainof an automatic transmission according to the present invention.

FIG. 5 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the third forward speed of a powertrainof an automatic transmission according to the present invention.

FIG. 6 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the fourth forward speed of a powertrainof an automatic transmission according to the present invention.

FIG. 7 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the fifth forward speed of a powertrainof an automatic transmission according to the present invention.

FIG. 8 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the sixth forward speed of a powertrainof an automatic transmission according to the present invention.

FIG. 9 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the seventh forward speed of apowertrain of an automatic transmission according to the presentinvention.

FIG. 10 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the eighth forward speed of a powertrainof an automatic transmission according to the present invention.

FIG. 11 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the first reverse speed of a powertrainof an automatic transmission according to the present invention.

FIG. 12 is a speed diagram that shows exemplary rotation speeds ofrespective operating members at the second reverse speed of a powertrainof an automatic transmission according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

As shown in FIG. 1, a powertrain of an automatic transmission accordingto various embodiments of the present invention includes an input shaft10, an output shaft 20, a transmission case 30, and first, second, andthird planetary gear sets PG1, PG2, and PG3.

The input shaft 10 receives a torque from an engine (not shown) througha torque converter (not shown).

The output shaft 20 outputs a torque from the powertrain.

The first planetary gear set PG1 is a double pinion planetary gear sethaving operating members of a first sun gear S1, a first ring gear R1,and a first planet carrier PC1. A first pinion gear P1 is connected tothe first planet carrier PC1 and gear-engaged with the first sun gear S1and the first ring gear R1 so that the first planet carrier PC1 rotatesby the rotation of the first pinion gear P1.

The second planetary gear set PG2 is a single pinion planetary gear sethaving operating members of a second sun gear S2, a second planetcarrier PC2, and a second ring gear R2. A second pinion gear P2 isconnected to the second planet carrier PC2 and gear-engaged with thesecond sun gear S2 and the second ring gear R2 so that the second planetcarrier PC2 rotates by the rotation of the second pinion gear P2.

The third planetary gear set PG3 is a double pinion planetary gear sethaving operating members of a third sun gear S3, a third ring gear R3,and a third planet carrier PC3. A third pinion gear P3 is connected tothe third planet carrier PC3 and gear-engaged with the third sun gear S3and the third ring gear R3 so that the third planet carrier PC3 rotatesby the rotation of the third pinion gear P3.

The first sun gear S1, the first ring gear R1, and the first planetcarrier PC1 is also called first, second, and third operating membersN1, N2, and N3 of a powertrain of an automatic transmission according tovarious embodiments of the present invention. The second sun gear S2,the second planet carrier PC2, and the second ring gear R2 is alsocalled fourth, fifth, and sixth operating members N4, N5, and N6 of apowertrain of an automatic transmission according to various embodimentsof the present invention. The third sun gear S3, the third ring gear R3,and the third planet carrier PC3 is also called seventh, eighth, andninth operating members N7, N8, and N9 of a powertrain of an automatictransmission according to various embodiments of the present invention.

The first planet carrier PC1 is fixedly connected with the input shaft10 and always acts as an input member. The third planet carrier PC3 isfixedly connected with the output shaft 20 and always acts as an outputmember. The first sun gear S1 is fixedly connected with the transmissioncase 30 and always acts as a fixed member.

The second ring gear R2 is fixedly connected with the third ring gearR3. The second planet carrier PC2 is fixedly connected with the thirdplanet carrier PC3. Therefore, since two pairs of operating members ofthe second and third planetary gear sets PG2 and PG3 are fixedlyconnected, four operational nodes are formed in speed diagrams as shownin FIG. 3 to FIG. 12.

A powertrain of an automatic transmission according to variousembodiments of the present invention utilizes a plurality of frictionmembers, in more detail, six friction members.

The plurality of friction members includes: a first clutch C1selectively connecting the third operating member N3 and the sixthoperating member N6; a second clutch C2 selectively connecting theseventh operating member N7 to the input shaft 10; a third clutch C3selectively connecting the second operating member N2 and the fourthoperating member N4; a fourth clutch C4 selectively connecting thesecond operating member N2 and the seventh operating member N7; a firstbrake B1 selectively connecting the sixth operating member N6 to thetransmission case 30; and a second brake B2 selectively connecting theseventh operating member N7 to the transmission case 30.

In more detail, the first clutch C1 selectively connects the firstplanet carrier and the second ring gear. The second clutch C2selectively connects the third sun gear to the input shaft. The thirdclutch C3 selectively connects the first ring gear and the second sungear. The fourth clutch C4 selectively connects the first ring gear andthe third sun gear. The first brake B1 selectively connects the secondring gear to the transmission case. The second brake B2 selectivelyconnects the third sun gear to the transmission case.

As shown in FIG. 2, an automatic transmission according to variousembodiments of the present invention realizes eight forward speeds andtwo reverse speeds by operating two friction members for respectiveshift-speeds.

In more detail, the third clutch C3 and the first brake B1 operate forthe first forward speed D1. The third clutch C3 and the second brake B2operate for the second forward speed D2. The third clutch C3 and thefourth clutch C4 operate for the third forward speed D3. The secondclutch C2 and the third clutch C3 operate for the fourth forward speedD4. The first clutch C1 and the third clutch C3 operate for the fifthforward speed D5. The first clutch C1 and the second clutch C2 operatefor the sixth forward speed D6. The first clutch C1 and the fourthclutch C4 operate for the seventh forward speed D7. The first clutch C1and the second brake B2 operate for the eighth forward speed D8. Thefourth clutch C4 and the first brake B1 operate for the first reversespeed R1. The second clutch C2 and the first brake B1 operate for thesecond reverse speed R2.

Formation of eight forward speeds and two reverse speeds by a powertrainof an automatic transmission according to various embodiments of thepresent invention is hereinafter described in detail.

Referring to FIG. 3 to FIG. 12, the first planet carrier PC1 alwaysacting as an input member always rotates at the rotation speed of theinput shaft 10. The first sun gear S1 is always stationary by beingfixedly connected to the transmission case 30. Therefore, speed diagramof the first planetary gear set PG1 remains the same regardless ofshift-speeds. That is, the first sun gear S1 is stationary, the firstplanet carrier PC1 rotates at the rotation speed of the input shaft 10,and the first ring gear R1 rotates at a reduced speed that is slowerthan the rotation speed of the input shaft 10.

The second ring gear R2 and the third ring gear R3 always rotate at thesame speed since they are fixedly connected with each other, and thesecond planet carrier PC2 and the third planet carrier PC3 always rotateat the same speed since they are fixedly connected with each other.

From such a constraint, the first to eighth forward speeds and tworeverse speeds are realized by selective operation of the first tofourth clutches C1 to C4 and the first and second brakes B1 and B2,which is hereinafter described in detail.

First Forward Speed

The third clutch C3 and the first brake B1 operate for the first forwardspeed D1.

The second sun gear S2 rotates at the reduced speed of the first ringgear R1 since the third clutch C3 operates. The second ring gear R2stops since the first brake B1 operates.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 3, and the first forward speed D1 isoutputted through the output member of the third planet carrier PC3.

Second Forward Speed

The third clutch C3 and the second brake B2 operate for the secondforward speed D2.

The second sun gear S2 rotates at the reduced speed of the first ringgear R1 since the third clutch C3 operates. The third sun gear S3 stopssince the second brake B2 operates.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 4, and the second forward speed D2 isoutputted through the output member of the third planet carrier PC3.

Third Forward Speed

The third clutch C3 and the fourth clutch C4 operate for the thirdforward speed D3.

The second sun gear S2 rotates at the reduced speed of the first ringgear R1 since the third clutch C3 operates. The third sun gear S3rotates at the reduced speed of the first ring gear R1 since the fourthclutch C4 operates. Both the second and third sun gears S2 and S3 rotateat the reduced speed, and thus the second and third planetary gear setsPG2 and PG3 integrally rotate at the reduced speed.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 5, and the third forward speed D3 isoutputted through the output member of the third planet carrier PC3.

Fourth Forward Speed

The second clutch C2 and the third clutch C3 operate for the fourthforward speed D4.

The second sun gear S2 rotates at the reduced speed of the first ringgear R1 since the third clutch C3 operates. The third sun gear S3rotates at the same speed with the input shaft 10 since the secondclutch C2 operates.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 6, and the fourth forward speed D4 isoutputted through the output member of the third planet carrier PC3.

Fifth Forward Speed

The first clutch C1 and the third clutch C3 operate for the fifthforward speed D5.

The second sun gear S2 rotates at the reduced speed of the first ringgear R1 since the third clutch C3 operates. The second ring gear R2rotates at the same speed with the input shaft 10 since the first clutchC1 operates.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 7, and the fifth forward speed D5 isoutputted through the output member of the third planet carrier PC3.

Sixth Forward Speed

The first clutch C1 and the second clutch C2 operate for the sixthforward speed D6.

The second ring gear R2 rotates at the same speed with the input shaft10 since the first clutch C1 operates. The third sun gear S3 rotates atthe same speed with the input shaft 10 since the second clutch C2operates. Both the second and third sun gears S2 and S3 rotate at thesame speed with the input shaft 10, the second and third planetary gearsets PG2 and PG3 integrally rotate at the rotation speed of the inputshaft 10.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 8, and the sixth forward speed D6 isoutputted through the output member of the third planet carrier PC3.

Seventh Forward Speed

The first clutch C1 and the fourth clutch C4 operate for the seventhforward speed D7.

The second ring gear R2 rotates at the same speed with the input shaft10 since the first clutch C1 operates.

The third sun gear S3 rotates at the reduced speed of the first ringgear R1 since the fourth clutch C4 operates.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 9, and the seventh forward speed D7is outputted through the output member of the third planet carrier PC3.

Eighth Forward Speed

The first clutch C1 and the second brake B2 operate for the eighthforward speed D8.

The second ring gear R2 rotates at the same speed with the input shaft10 since the first clutch C1 operates. The third sun gear S3 stops sincethe second brake B2 operates.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 10, and the eighth forward speed D8is outputted through the output member of the third planet carrier PC3.

First Reverse Speed

The fourth clutch C4 and the first brake B1 operate for the firstreverse speed R1.

The third sun gear S3 rotates at the reduced speed of the first ringgear R1 since the fourth clutch C4 operates. The second ring gear R2stops since the first brake B1 operates.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 11, and the first reverse speed R1 isoutputted through the output member of the third planet carrier PC3.

Second Reverse Speed

The second clutch C2 and the first brake B1 operate for the secondreverse speed R2.

The third sun gear S3 rotates at the same speed with the input shaft 10since the second clutch C2 operates. The second ring gear R2 stops sincethe first brake B1 operates.

Therefore, speed diagram of the second and third planetary gear sets PG2and PG3 is formed as shown in FIG. 12, and the second reverse speed R2is outputted through the output member of the third planet carrier PC3.

FIG. 2 shows an example of available speed ratios of the eight forwardspeeds and two reverse speeds. Such an example figures of speed ratiosare obtained in connection with a case that the number of teeth of thesun and ring gears of the first planetary gear set PG1 are respectively10 and 25, the number of teeth of the sun and ring gears of the secondplanetary gear set PG2 are respectively 10 and 18, and the number ofteeth of the sun and ring gears of the third planetary gear set PG3 arerespectively 10 and 32.

However, it should not be understood that the scope of the presentinvention is limited thereto. A variety of speed ratios may be obtainedby modifying the number of teeth of the sun and ring gears of the first,second, and third planetary gear sets PG1, PG2, and PG3.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

1. A powertrain of an automatic transmission comprising: a firstplanetary gear set having a first operating member fixedly connected toa transmission case, a second operating member, and a third operatingmember fixedly connected to an input shaft; a second planetary gear sethaving a fourth operating member selectively connected to the secondoperating member, a fifth operating member, and a sixth operating memberselectively connected to the third operating member and the transmissioncase; a third planetary gear set having a seventh operating memberselectively connected to the second operating member, the input shaft,and the transmission case, an eighth operating member fixedly connectedto the sixth operating member, and a ninth operating member fixedlyconnected to the fifth operating member and an output shaft; and aplurality of friction members that selectively connect operating membersof the first, second, and third planetary gear sets, the input shaft,and the transmission case.
 2. The powertrain of claim 1, wherein theplurality of friction members comprise: a first clutch selectivelyconnecting the third operating member and the sixth operating member; asecond clutch selectively connecting the seventh operating member to theinput shaft; a third clutch selectively connecting the second operatingmember and the fourth operating member; a fourth clutch selectivelyconnecting the second operating member and the seventh operating member;a first brake selectively connecting the sixth operating member to thetransmission case; and a second brake selectively connecting the seventhoperating member to the transmission case.
 3. The powertrain of claim 1,wherein the first planetary gear set is a double pinion planetary gearset having operating members of a first sun gear, a first ring gear, anda first planet carrier, the first sun gear acting as the first operatingmember, the first ring gear acting as the second operating member, andthe first planet carrier acting as the third operating member.
 4. Thepowertrain of claim 1, wherein the second planetary gear set is a singlepinion planetary gear set having operating members of a second sun gear,a second planet carrier, and a second ring gear, the second sun gearacting as the fourth operating member, the second planet carrier actingas the fifth operating member, and the second ring gear acting as thesixth operating member.
 5. The powertrain of claim 1, wherein the thirdplanetary gear set is a double pinion planetary gear set havingoperating members of a third sun gear, a third ring gear, and a thirdplanet carrier, the third sun gear acting as the seventh operatingmember, the third ring gear acting as the eighth operating member, andthe third planet carrier acting as the ninth operating member.
 6. Thepowertrain of claim 2, wherein: the third clutch and the first brakeoperate for a first forward speed; the third clutch and the second brakeoperate for a second forward speed; the third clutch and the fourthclutch operate for a third forward speed; the second clutch and thethird clutch operate for a fourth forward speed; the first clutch andthe third clutch operate for a fifth forward speed; the first clutch andthe second clutch operate for a sixth forward speed; the first clutchand the fourth clutch operate for a seventh forward speed; the firstclutch and the second brake operate for an eighth forward speed; thefourth clutch and the first brake operate for a first reverse speed; andthe second clutch and the first brake operate for a second reversespeed.
 7. The powertrain of claim 1, wherein: the first planetary gearset is a double pinion planetary gear set having operating members of afirst sun gear, a first ring gear, and a first planet carrier, the firstsun gear acting as the first operating member, the first ring gearacting as the second operating member, and the first planet carrieracting as the third operating member; the second planetary gear set is asingle pinion planetary gear set having operating members of a secondsun gear, a second planet carrier, and a second ring gear, the secondsun gear acting as the fourth operating member, the second planetcarrier acting as the fifth operating member, and the second ring gearacting as the sixth operating member; and the third planetary gear setis a double pinion planetary gear set having operating members of athird sun gear, a third ring gear, and a third planet carrier, the thirdsun gear acting as the seventh operating member, the third ring gearacting as the eighth operating member, and the third planet carrieracting as the ninth operating member.
 8. The powertrain of claim 7,wherein the plurality of friction members comprise: a first clutchselectively connecting the first planet carrier and the second ringgear; a second clutch selectively connecting the third sun gear to theinput shaft; a third clutch selectively connecting the first ring gearand the second sun gear; a fourth clutch selectively connecting thefirst ring gear and the third sun gear; a first brake selectivelyconnecting the second ring gear to the transmission case; and a secondbrake selectively connecting the third sun gear to the transmissioncase.
 9. The powertrain of claim 8, wherein: the third clutch and thefirst brake operate for a first forward speed; the third clutch and thesecond brake operate for a second forward speed; the third clutch andthe fourth clutch operate for a third forward speed; the second clutchand the third clutch operate for a fourth forward speed; the firstclutch and the third clutch operate for a fifth forward speed; the firstclutch and the second clutch operate for a sixth forward speed; thefirst clutch and the fourth clutch operate for a seventh forward speed;the first clutch and the second brake operate for an eighth forwardspeed; the fourth clutch and the first brake operate for a first reversespeed; and the second clutch and the first brake operate for a secondreverse speed.